Thermographic recording process for reproducing continuous tone transparencies

ABSTRACT

A PROCESS FOR RESPONDING INFORMATION WHEREIN A HEATSENSITIVE RECORDING LAYER ADAPTED TO CHANGE THE WATERPERMEABILITY THEREOF WHEN HEATED AND CONTAINING UNIFORMLY DISTRIBUTED THERETHROUGH FINELY-DIVIDED MATERIAL ABSORBING VISIBLE RADIATION AND CONVERTING THE SAME TO HEAT IS EXPOSED TO RADIATION THROUGH A CONTINUOUS TONE TRANSPARENCY TO BE REPRODUCED AND A SCREEN, THE TIME OF THE EXPOSURE BEING NOT MORE THAN ONE-TENTH OF A SECOND, AND THE INTENSITY OF THE RADIATION BEING SUFFICIENT TO PRODUCE IN THE EXPOSED PORTIONS OF THE RECORDING LAYER SUFFICIENT HEAT TO BRING ABOUT THE CHANGE IN ITS WATER-PERMEABILITY,   AND THE EXPOSED RECORDING LAYER IS TREATED WITH AN AQUEOUS LIQUID TO DEVELOP THE INFORMATION THEREIN.

Feb. 16,1971 N, VRANCKE 3,564,597

THERMOGRAPHIC RECORDING PROCESS FOR REPRODUCING CONTINUOUS TONETRANSPARENCIES Filed Jan. 11, 1967 2 Sheets-Sheet 1 ZNVENTOR' 31 WWMWATTORNEY Feb. 16, 19 71 7 N VRANCKEN. i 3,564,597

: 'THERMOGRAPHIC RECORDING PROCESS FOR REPRODUCING CONTINUOUS TONE'I'RANSPARENCIES" Filed Jan. 11, 1967- 2 sheets-sheet'z 7? INVENT R WaMLdea-4 ATTORNEY United States Patent 3,564,597 THERMOGRAPHIC RECORDINGPROCESS FOR REPRODUCING CONTINUOUS TONE TRANSPARENCIES Marcel NicolasVrancken, Hove, Belgium, assignor to Gevaert-Agfa N.V., Mortsel,Belgium, a Belgian comp y Filed Jan. 11, 1967, Ser. No. 608,572 Claimspriority, application Great Britain, Jan. 11, 1966, 1,351/ 66 Theportion of the term of the patent subsequent to Nov. 4, 1986, has beendisclaimed Int. Cl. G03b 41/00 U.S. Cl. 250-65 12 Claims ABSTRACT OF THEDISCLOSURE A process of reproducing information wherein a heatsensitiverecording layer adapted to change the waterpermeability thereof whenheated and containing uniformly distributed therethrough finely-dividedmaterial absorbing visible radiation and converting the same to heat isexposed to radiation through a continuous tone transparency to bereproduced and a screen, the time of the exposure being not more thanone-tenth of a second, and the intensity of the radiation beingsufiicient to produce in the exposed portions of the recording layersuificient heat to bring about the change in its water-permeability, andthe exposed recording layer is treated with an aqueous liquid to developthe information therein.

The present invention relates to a method of making screenedreproductions from a continuous-tone transparency on heat-sensitivematerials. Up to now thermographic copying materials were onlyconsidered to be useful for the reproduction of documents and line work.

Line work applies to those originals, which comprise but pure white anddeep black, such as typed and printed texts, pen drawings, etc.

Continuous-tone work, however, applies to originals, which besides blackand white may also comprise the whole range of intermediate gray tones,as e.g. in silver image negatives of soft gradation.

Continuous-tone work can be reproduced on very contrasty silver halideemulsion layers known in the graphic art by use of a screeningtechnique, which consists in printing the continuous-tone originaltogether with a screen. In screening technique two types of screens arecommonly used viz. glass-screens and contact screens. In practice theuse of a contact screen is simpler and more economical than the use of aglass screen.

On exposure the contact screen is placed in contact with thelight-sensitive material. Due to the modulation of the continuous-tonetransparency and the characteristics of the contact screen dots, theoriginal is reproduced on a very contrasty copying material as a largenumber of very small dots the size of which is determined depending onthe luminosity of the corresponding parts of the continuous-tonetransparency.

According to the present invention, a latent or visible screen image ofa continuous tone transparency is produced by exposing toelectromagnetic radiation, through such transparency and a screen, aheat-sensitive recording layer containing substance(s) which become(s)heated by the irradiation and consequently bring(s) about a physicaland/or chemical change in the said layer, the exposure being for suchbrief time that heating sufficient to effect such change does not occurin any areas of such layers as a result of heat conduction from thematerial of the screen.

3,564,597 Patented Feb. 16, 1971 The radiation used may be infrared and/or visible light radiation provided that the composition of theheat-sensitive layer is appropriately chosen. For a disclosure ofheatsensitive layers which respond to such different types ofirradiation we refer to the specifications filed in the published Dutchpatent application 64/ 14226 filed Dec. 7, 1964 by GevaertPhoto-Producten N.V., the published Dutch patent application 66/06719filed May 17, 1966 and in the published Dutch patent application 66/08711 filed June 23, 1966 both by Gevaert-Agfa N.V. which should be readin conjunction herewith.

The invention is particularly but not exclusively concerned with usingheat-sensitive layers the composition of which undergoes a decrease insolubility in water when irradiated so that after image-wise irradiationthe non irradiated areas can be washed away so that a relief imageresults.

Provided that a high intensity radiation is emitted by the radiationsource, it is easily possible to avoid heating of the heat-sensitivelayer by heat conduction from the screen since the exposure time can beof such short duration that there is insuflicient time for such heatconduction to take place.

It is more particularly intended to perform the invention usingradiation composed wholly or mainly of light such as, e.g., is emittedby'fiash lamps, and to employ as heat-sensitive layer a layer containinglight-absorbing substance (s) that convert the light into heat and theinvention will hereafter be more particularly described in that form.The following more detailed description of the invention moreover hasreference to embodiments in which the screen dots of a contact screenare held in direct contact with the heat-sensitive layer during theexposure since this is recommended for obtaining very sharp screenedreproductions but it is not absolutely essential for the invention forsuch direct contact to exist since a thin interlayer may, e.g., bepresent.

It has been found that when a thermo-sensitive layer containingsufficiently light-absorbing substance(s) that convert that light intoheat is subjected to a very short contact-exposure to light of very highintensity through a continuous-tone transparency in contact with acontact screen, a very sharp screened print of the continuous-tonetransparency can be obtained due to the very locally internally producedheat in the said substance(s).

A too high absorption of light and corresponding too high production ofheat in the screen dots of the contact screen and image areas of theoriginal (which excessive heat due to the contact of the screen dotswith the thermosensitive layer would be transferred by conductionthereto if a relatively long exposure time was applied), can be avoidedby a high intensity very short exposure, particularly when forming ascreen image of a continuous-tone transparency of rather low density andusing a corresponding contact screen. In this way very sharp highdensity screened prints possessing the complete tone scale of thecontinuous-tone transparency can be obtained. It is advisable whencopying silver image transparencies for the image density to be belownormal. A normal density silver transparency can be reduced in densityprior to being used by a conventional reducer solution. It is alsorecommendable to use a contact screen of which the silver dots are ofless density than normal.

The use of a rather low density continuous-tone transparency makes itpossible to avoid damage of the transparency image by absorbed heat inthe silver metal parts (burning ofthe gelatin binder) and offers a moreeconomical use of the light emitted from the light source, since it isthe image-wise transmitted light which produces the desired change inthe recording layer.

It is self-explanatory that according to the exposure technique of thepresent invention the copying light absorbed in the said light-absorbingsubstance (s) present internally in the thermo-sensitive layer producetherein the desired image differentiation based on a heat-induced and/or promoted chemical and/ or physical change.

In order to achieve a very true reproduction of the tone scale of thecontinuous-tone transparency, the maximum density in the dots of thecontact-screen should not be substantially different from the maximumdensity of the transparency and is preferably equal thereto. Preferablythe maximum optical density of the continuous-tone transparency iscomprised between 0.2 and 1.0.

The composition of the heat-sensitive layer and the kind of physicaland/ or chemical change obtained therein on heating determines whether adirect visible image or latent image developable by an after-treatmentwill be obtained.

For suitable heat-sensitive layers we particularly refer toheat-sensitive gelatin layers such as the heat-sensitive gelatin layersdescribed in the published Dutch patent application 66/08711 filed June23, 1966 by Gevaert-Agfa N.V., the exposed gelatin parts of whichpossess an increased water-permeability, water-solubility andswellability in water.

For a good differentiation in water-permeability and water-solubilityheat-sensitive recording layers of the gelatin type preferably containat least 80% by weight of gelatin.

Other suitable heat-sensitive layers are mainly cOmposed of polyvinylalcohol and the heat-exposed parts of such layers show a decrease inwater-solubility and waterpermeability in respect of the unexposedareas. As disclosed in published Dutch patent application 66/016-17filed Feb. 9, 1966 by Gevaert-Agfa N.V. vinyl polymers containing atleast 95% of vinyl alcohol units are suited.

Good results can also be obtained using hydrophilic colloid layerscontaining in a weight ratio of at least 1:1 in respect of the colloiddispersed particles of a hydrophobic thermoplastic polymer and showingin heated areas a decrease in water-permeability, hydrophility andwatersolubility, as is disclosed in published Dutch patent application64/14226 filed Dec. 7, 1964 by Gevaert Photo- Producten N.V. andpublished Dutch patent application 66/06719 filed May 17, 1966 byGevaert-Agfa N.V.

The recording layer is preferably for at least 50% by Weight composed ofthe dispersion consisting of the said hydrophobic thermoplastic polymerparticles in said colloid or hydrophilic binder.

The heat-sensitive recording layers for use in the recording processaccording to the present invention preferably adsorb at least 80% of thelight passing through the sandwich of continuous-tone transparency andcontact screen.

According to a preferred copying technique of the present inventionheat-sensitive materials of the type described in the latter publishedDutch patent application 66/06719 filed May 17, 1966 by Gevaert-AgfaN.V. are used, such material preferably having a heat-sensitive layerwherein copying light-absorbing substances are dispersed in such anamount that an optical density of at least 1 is obtained.

Heat-sensitive materials on the basis of gelatin as de scribed in thepublished Dutch patent application 66/ 08711 filed June 23, 1966 byGevaert-Agfa N.V. are suited for positive-positive printing, in otherwords for produc ing by a selective washing away of water-solubleportions a positive screen transparency of a positive continuoustonetransparency, whereas heat-sensitive materials on the basis of adispersion of latex particles, which are solid at room temperature in ahydrophilic colloid binder as described in the published Dutch patentapplication 66/ 06719 filed May 17, 1966 by Gevaert-Agfa N.V. are suitedfor negative-positive printing.

Substances absorbing infra-red light and visible light and which aresuited for being incorporated into the thermo-sensitive layer assubstances converting that light into heat are described, e.g., inpublished Dutch patent application 66/06719 filed May 17, 1966 andpublished Dutch patent application 66/08711 filed June 23, 1966 both byGevaert-Agfa N.V. As visible light and infra-red absorbing substances wewould particularly mention finely divided carbon black, graphite,prussian blue, oxides, sulphides or carbonates of heavy metals having anatomic weight between 45 and 210, such as manganese or lead sulphide orthese heavy metals themselves in finely divided state e.g. silver,bismuth, lead, iron, cobalt and nickel. The particle size of thesesubstances preferably should not exceed 0.1,u.

When using visible copying light the reproduction process of the presentinvention is not limited to the reproduction of black-and-whitetransparencies. Monochromatic transparencies can be reproduced by usingin the heatsensitive material substance(s) absorbing light correspondingto the colour of the original or light of a colour complementary to thecolour of the original.

Thus, according to a particular embodiment the heatsensitive materialcan be made sensitive to light of a limited range of wavelengths. Thiscan be done by incorporating into the heat-sensitive layer colouredsubstances, which absorb light of a particular part of the visiblespectrum and convert that light into heat. Examples of such layers andingredients therefor are given in the published Dutch patent application66/06719 filed May 17, 1966 by Gevaert-Agfa N.V. wherein spectrallysensitized heat-sensitive layers are described for recording colouredoriginals in terms of differences in water-solubility and swellingtendency.

It is to be understood that mixtures of said coloured substances can beused too, so that light of the whole visible spectrum is absorbed. Thesaid substances have not necessarily to absorb in the range of thevisible spectrum alone, they may also absorb infrared light to a more orless extent.

The coloured substance or mixtures of said substances converting lightinto heat and optically sensitizing the heat-sensitive materials arepreferably light-absorbing corresponding to at least one of the primarycolours (red, green, blue) or subtractive colours (cyan, magenta,yellow).

Substances that absorb visible light of a part of the visible spectrumand wherein absorbed light energy is converted into heat are e.g. dyesbelonging to the classes of the azo dyes, the triarylmethane dyes, thexanthene dyes, the acridine dyes, the methine dyes, the azine dyes, thephthalocyanine dyes, the anthraquinone dyes and allied dyes. Said dyescan be used in dispersed as well as in dissolved form.

Preferably they are present in such an amount that an optical density ofat least 1 is attained.

It is recommendable to use a heat-sensitized recording material that canbe processed by plain water (selective image-wise washing away ofwater-soluble portions of the recording layer).

A preferred recording material in that respect comprises aheat-sensitive recording layer that incorporates thermoplastichydrophobic polymer particles which are solid at room temperature andare dispersed in a weight ratio of at least 1:1 in a water-solublebinder. The recording layer is coated on an interlayer orself-supporting sheet which is composed of or comprises hydrophobicsubstance(s) having a melting or softening point lower than, equal to,or not substantially higher than that of the hydrophobic thermoplasticparticles present in the recording layer.

We particularly prefer to use a heat-sensitive recording material asjust described and comprising an interlayer which contains suchhydrophobic substances dispersed in a hydrophilic binder which is lesssoluble in water than the hydrophilic binder of the recording layer. Asspecific examples poly-N-vinylpyrrolidone may be used as binder for therecording layer and gelatin as binder for the interlayer orself-supporting. sheet.

Continuous-tone transparencies, which are specially suited for beingreproduced according to the present invention by means of recordingmaterials described in published Dutch patent application 66/06719 filedMay 17, 1966 and published Dutch patent application 66/ 08711 filed June23, 1966 both by Gevaert-Agfa N.V. have a maximum optical density notexceeding 0.5. The exposure time preferably does not exceed 10- sec.

Suitable radiation sources producing copying light of high intensity ina very small lapse of time and which are very suited for use inprocesses according to the present invention are the so-called flashlamps. Good results are obtained with xenon gas discharge lamps, Whichcan supply a light energy of 100 to 1000 watts sec. in a time intervalof l to seconds. These flash lamps emit a greater part of energy asvisible light together with infra-red light. Details about a copyingapparatus containing such a discharge lamp can be found in Belgianpatent specification 664,868 filed June 3, 1965 by Agfa-Gevaert AG.

Evidently gas discharge lamps with a much lower energy output can beused if the emitted energy is focused onto a relatively smallheat-sensitive area. So, e.g. a gas discharge lamp with an energy outputof 40 watt sec. is suited for copying 6 cm. x 6 cm. and 6 cm. x 9 cm.originals onto heat-sensitive materials as described in published Dutchpatent application 66/06719 filed May 17, 1966 by Gevaert-Agfa N.V. Inpractice, for such materials having an optical density of at least 1, alight energy of 0.3 watt sec. per sq. cm. will suffice for the desiredimage-differentiation. It is further self-explanatory that exposure maybe performed progressively and/or intermittently. In other words therecording material may be scanning-wise exposed, e.g. by ahigh-intensity light spot rapidly line-wise scanning the recordingmaterial, or may be progressively exposed through a slot wherein, e.g.,light of a tube-like radiation source is focused.

It is evident that the heat-sensitive material, before or during thecreation of the image-wise heat difierentiation, can if desired besubjected to overall heating to a certain temperature below thetemperature of image differentiation in the heat-sensitive material.

The following examples illustrate the present invention.

EXAMPLE 1 A poly(ethylene terephthalate) support of 0.1 mm. thicknessprovided with a subbing layer is coated with the following compositionpro rata of 30 g./sq. m.:

After drying, the material possesses an optical density of 3.5 measuredby transmittance. The material is exposed as schematically representedin FIG. 1, to a xenon gas discharge lamp having a capacity of 1000 wattsec.

and producing light in a time of V2000 sec., through a continuous-tonenegative transparency and a contact screen, each having a maximumoptical density of 0.5.

In FIG. 1 element No. 1 represents the transparent support of acontinuous-tone transparency of which the element 2 is the image-bearinglayer. Element No. 3 represents the transparent support of a contactscreen and element No. 4 represents the layer containing the contactscreen dots. Element No. 5 represents the heat-sensitive layercontaining the substances absorbing copying light and thermoplasticpolymer particles and element No. 6 represents a transparent support forthat layer.

After exposure, whereby the exposed areas are rendered relativelywater-insoluble, the material is dipped into water and gently rubbedwith a cotton pad. The heatsensitive layer is removed in the non-exposedareas.

A positive very true image of the continuous-tone transparency isobtained consisting of tiny dots with an equal optical density varyingin diameter.

The same results are obtained when the polyethylene dispersion mentionedhereinbefore is replaced by a 40% aqueous dispersion of poly(vinylchloride) particles sizing on the average 0.16;. and having a molecularweight of 200,000 or a 40% aqueous dispersion of polystyrene particlessizing on the average 0.13 and having a molecular weight of 50,000.

EXAMPLE 2 A paper support weighing g./ sq. m. provided with a barytacoating is covered pro rata of 50 g./sq. m. with the followingcomposition:

10% aqueous dispersion of gelatin 200 10% aqueous dispersion ofcolloidal silver 600 40% dispersion of polyethylene as described inExample 1 240 3% aqueous solution of the sodium salt of the condensationproduct of oleic acid and methyltaurine 40 10% aqueous solution ofsaponin 40 When dried, the material is exposed as described in Example1.

Subsequently the material is dipped in a conventional silver-bleachingbath.

A positive high density screen image of the negative continuous-tonetransparency is obtained.

EXAMPLE 3 A cellulose triacetate support of 0.14 mm. thickness providedwith a gelatin subbing layer is coated with the following composition:

When dried, the material is exposed as schematically represented in FIG.2. The same continuous-tone transparency is used as described in Example1, but the material is non-differentially preheated to 70 C.

In FIG. 2 the element No. 1 represents the transparent support of acontinuous-tone silver image transparency and element No. 2 the layercontaining the silver image. Element No. 3 represents the transparentsupport of a magenta contact screen and element No. 4 the layercontaining the screen dots. Element No. 5 represents the heatsensitivelayer and element No. 6 the transparent support therefor. Element No. 7is a heating jacket and element No. 8 the flash exposure lamp, which isa xenon gas discharge lamp producing light with an intensity of 1000Watt. sec. in V3000 sec. The elements No. 9 are the electrodes of thatlamp. On exposure, the elements 1 to 7 are concentrically arrangedaround the flash exposure lamp, the axis of which is situated at adistance of 4 cm. from the continuous-tone transparency.

After exposure, the recording material is dipped in water of 20 C. andgently rubbed with a wadding of cotton. The portions of theheat-sensitive layer corresponding with the non-exposed areas areremoved.

A positive magenta screen image of the negative continuous-tonetransparency is obtained.

EXAMPLE 4 A cellulose triacetate support of 0.12 mm. thickness providedwith a subbing layer for gelatin is coated with the followingcomposition pro rata of 50 g./sq. m.:

% aqueous solution of sodium-tetradecylsulphate The layer is dried at 20C. The copying material thus obtained is exposed as described in Example1 but through a positive transparency having a maximum density of 0.3and a silver-contact screen having a maximum density of 0.3. Afterexposure, the material is dipped into water of 20 C. and gently rubbed.The heat-sensitive layer is removed in the exposed areas.

A very true positive copy of the positive transparency is obtained.

What we claim is:

1. A process of reproducing information which comprises the steps ofcontact exposing to visible light through a continuous tone transparencyto be reproduced having a maximum optical density between about 0.2 and1.0 and a contact screen having a maximum optical density not greaterthan that of said transparency, a normally waterremovble heat-sensitiverecording layer adapted to undergo a loss in water-removability uponheating, said layer comprising particles of at least on hydrophobicthermoplastic polymer dispersed in a film of a hydrophilic binder in aratio of at least 1:1 by weight and containing uniformly distributedtherethrough finely-divided material absorbing such radiation andconverting the same into heat in sufficient amount that the layerabsorbs at least 80% of the copying light impinged thereon, saidexposure being of a time not exceeding one-tenth of a second and of suchintensity as to produce in a screen dot pattern of exposed regions ofsaid recording layer sufficient heat through the absorption thereby bysaid finely-divided material to render said dot pattern water-insolublebut not such as to significantly reduce the water-removability of theunexposed regions of said layer, and treating said layer with an aqueousliquid to remove the unexposed regions therefrom.

2. The process of claim 1 wherein the amount of visible light absorbingmaterial is sufficient to impart to said recording layer an opticaldensity of at least about 1.

3. The process of claim 2 wherein said light has an intensity of atleast about 0.3 watt sec. per sq. cm.

4. The process of claim 1 wherein said transparency has an opticaldensity not greater than 0.5.

5. A process for reproducing information according to claim 1, whereinthe recording layer is exposed by means of a flash lamp emitting visiblelight.

6. A process for reproducing information according to claim 5, whereinthe exposure is carried out with a xenon gas discharge lamp supplying alight energy of 100 to 1000 Watt sec. in a time interval of 10- to 10-seconds.

7. A process for reproducing information according to claim 1, whereinthe said copying light-absorbing substances that convert light into heatare dispersed carbon particles.

8. A process for reproducing information according to claim 1, whereinthe said copying light-absorbing substances that convert light into heatare dispersed silver metal particles.

9. A process for reproducing information according to claim 1, whereinthe hydrophilic binder is a water-soluble polymer.

10. A process for reproducing information according to claim 9, whereinthe water-soluble polymer is poly(N-vinylpyrrolidone) or gelatin.

11. A process for reproducing information according to claim 1, whereinthe recording layer contains at least by weight of gelatin.

12. A process for reproducing information according to claim 1, whereinthe recording layer mainly contains a polyvinyl polymer containing atleast by weight of vinyl alcohol units.

References Cited UNITED STATES PATENTS 3,010,391 11/1961 Buskes et al.96'45X 3,223,838 12/1965 Hoshino et al 25065(1) 3,298,833 1/1967 Gaynor96-27 3,392,020 7/1968 YutZy et al 96-67 OTHER REFERENCES Van derGrinten Bulletin, Aug. 1, 1963, pp. 5 and 6.

A. L. BIRCH, Assistant Examiner US. Cl. X.R. 96-45

